1. Field of the Invention
The present invention relates to a disk reproducing device which reproduces signals recorded on such a disk as optical disk. In particular, the present invention relates to a disk reproducing device appropriate for reproduction of signals recorded on one disk written by means of a plurality of writing devices.
2. Description of the Background Art
There has been a technique of making a recording, on a disk on which multisession recording is possible, in sessions respectively by a plurality of recording devices.
Two techniques are disclosed, for example, concerning reproduction of a disk which has been recorded by means of a plurality of recording devices. One is disclosed in Japanese Patent Laying-Open No. 9-306005, according to which characteristics of a servo circuit of a reproducing device are self-adjusted for each of regions of the disk that are recorded respectively by different recording methods. The other is disclosed in Japanese Patent Laying-Open No. 2001-344911 according to which data are recorded on the same recording medium in accordance with a plurality of reproduction specifications and reproduction information is further recorded on the recording medium in order to reproduce the data in accordance with respective reproduction specifications.
The above-described conventional techniques, however, do not consider error correction for the disk or unsatisfactory in terms of the error correction. Concerning error correction, Japanese Patent Laying-Open No. 2000-276848 for example discloses a technique of error correction by which errors are corrected by changing an equalizing factor depending on whether a reproduction signal has asymmetry or not.
Japanese Patent Laying-Open No. 2000-276848 discloses a technique of reproducing data by PRML (Partial Response Maximum Likelihood) which is a reproduction system of digital data and is a combination of the partial response system and the maximum likelihood decoding system using the Viterbi decoding system. Specifically, with reference to FIG. 9, an optical disk is irradiated with laser light, accordingly digital data recorded on the optical disk medium is read as an analog reproduction signal and the reproduction signal is amplified by a preamplifier circuit 104. Then, the amplified analog signal is shaped by a waveform shaping circuit 105 having functions of a low-pass filter (LPF) and an equalizer (EQ) conducting waveform shaping, and converted into a digital signal by an analog/digital (A/D) converting circuit 106. The digitized reproduction signal is further equalized to a waveform of partial response characteristics (PR characteristics) that is set in advance by an equalizer 111. An output signal from equalizer 111 is Viterbi-decoded by a maximum likelihood decoding circuit 120 so as to reproduce the digital data recorded on the optical disk.
The reproduction system shown in FIG. 9, however, requires the read analog signal, to be converted into digital data and processed by equalizer 111 and maximum likelihood decoding circuit 120.
There has always been a need for simplification of the disk reproducing device.